Electrodeposition of chromium and anti-misting agents therefor



United States Patent 3,342,709 ELECTRODEPOSITION 0F CHROMIUM AND ANTI-MISTING AGENTS THEREFOR Andy Albert Johnson, Oak Park, Mich., assignor to M & T

Chemicals Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Sept. 24, 1963, Ser. No. 311,243 21 Claims. (Cl. 204-51) This invention relates to chromium plating. More particularly it relates to a novel technique for suppressing the evolution of fumes from chromium plating baths.

As is well known to those skilled in the art, chromium plating may be effected from baths which contain chromic acid and sulfate (typically introduced as sulfuric acid) together with other ingredients or additives including those which may control or regulate the plating characteristics of the bath. Typical of such regulating additives may be strontium sulfate and potassium silicofluoride with or without additions of excess strontium ion (introduced as SrCO SrCrO,, etc.) of excess potassium ion (introduced as K CrO K Cr O- etc.) which may make the bath a high speed bath which is self-regulating with respect to catalyst anion.

During chromium plating from such baths, there is a very vigorous evolution of hydrogen from the cathode and of oxygen from the anode; as these gases escape, they carry into the atmosphere substantial amounts of en trained chromium plating solution containing chromic acid, hydrofluoric acid, sulfuric acid, etc. sufiicient to produce a variety of toxic effects on personnel engaged in the operation of the bath. Cumulative effects of these fumes may cause irritation of the respiratory tract, perforation of the nasal septum or lung cancer.

The evolved gases together with the entrained chemicals therefore pose a serious problem. Particularly because they are toxic to operating personnel and because they are also corrosive to equipment or harmful to other nearby plating baths, such as that used to plate nickel, it is desired to operate in a manner to minimize or eliminate the evolution of the objectionable constituent of these gases into the surrounding atmosphere. Prior art attempts to accomplish these desiderata by means of mist-suppressing organic additives have been only partially successful. Most of the prior art additives have been organic surfactants which operate by building up a high head of foam on the chromium plating bath restricting the entrainment of liquids in the evolved hydrogen and oxygen. As operations continue, the foaming properties of these prior art additives decreases, mainly because they deteriorate or decompose under the severe action of the electrolyte. As a result, their value as fume suppressants may decrease.

Those skilled in the art have attempted to develop inexpensive fume suppressants characterized by a long life during which the composition may permit maintenance of a fixed, predetermined blanket of foam on the surface of the plating bath. Attempts have also been made to develop a fume suppressant which was not characterized by the fact that the inadvertent or accidental addition of an excess of material might result in an excess of foam which might result in overflow of the dangerously corrosive contents of the bath or which, because said foam contained a mixture of hydrogen and oxygen, might react implosively when ignited by the electrical arcing commonly encountered in the plating operation.

It is an object of this invention to provide a novel fume suppressant system for electroplating baths characterized by its ability to economically generate a foam blanket of controlled thickness. Other objects will be apparent to those skilled in the art on inspection of the following description.

3,342,709 Patented Sept. 19, 1967 "ice In accordance with certain of its aspects. the novel composition of this invention which is characterized by its ability to controllably develop and maintain over an extended period of time a fixed predetermined optimum thickness of foam may comprise an anti-misting amount of a mixture of a sulfonated 2-alkylbenzimidazole and a disulfonated alkyl diphenyl oxide.

In accordance with certain other aspects of this invention, it may be possible to effect chromium plating in a bath containing chromic acid and sulfate wherein substantial quantities of gas may be liberated from the electrodes by the process which comprises maintaining a chromium plating bath containing chromic acid and sulfate, maintaining therein an anti-misting amount of a mixture of a sulfonated Z-alkylbenzimidazole and a disulfonated alkyl diphenyl oxide, and plating chromium onto a cathode in said bath.

Typically chromium plating baths with which this invention may be employed may commonly have the following illustrative composition.

The novel fume suppressant or anti-misting agent of this invention may include a disulfonated alkyl diphenyl oxide, typically having the following formula:

wherein R is a hydrocarbon radical having 6-18 carbon atoms, n is 0-1, and X is a cation selected from the group consisting of hydrogen, ammonium and metals.

Typical R radicals which may be employed may be alkyl radicals including hexyl, octyl, nonyl, dodecyl, and octadecyl radicals. preferably octyl, nonyl, and dodecyl radicals. The R radicals may preferably be the same. X may typically include sodium, ammonium, hydrogen, potassium, lithium, trivalent chromium, calcium, strontium, barium, magnesium, nickel, iron. and copper. X may preferably be ammonium or alkali metal eg sodium, potassium, and lithium.

The sulfonated alkyl diphenyl oxide in the highly acid and strongly oxidizing bath is believed to exist in the form of the acid radical having the formula a. sor

The sulfonated alkyl diphenyl oxide as produced and utilized may be a mixture of compounds containing the noted substituents. In a typical commercial mixture, such as that available under the trademarks DOWFAX 2A1 or BENAX 2A1, the sulfonic acid groups may be primarily substituted in the position ortho to the etherbearing carbon, and the alkyl chain may be primarily substituted in the position para to that carbon. The commercial product may be a mixture of monoand dialkyl substituted products. A preferred composition may be a mixture of the disulfonated salts of monododecyl diphenyl oxide and didocecyl diphenyl oxide. The disodium and dipotassium salts may be preferred.

The novel fume-suppressant or anti-misting agent of this invention may include a compound which may typically have the structure wherein Ar is selected from the group consisting of phenyl and naphthyl rings, said ring being incorporated into the imidazole structure through vicinal carbon atoms of said ring; M is a cation selected from the group consisting of hydrogen, ammonium and metals; R is a non-aromatic hydrocarbon radical containing at least 3 carbon atoms; R" is selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, omega-sulfonated alkyl, sulfonated 20 aryl, and sulfonated aralkyl; R' is selected from the group consisting of hydrogen, alkyl and aralkyl; Y is a water-soluble anion; and a is 0-1. The sulfonated benzimidazoles which contain alkenyl, cycloalkyl and cycloalkenyl substituents in the 2-position will be understood to be embraced by the term sulfonated 2-alkyl benzimidazole as used in the context of this invention.

In the compounds having the above structure, the group Ar may be phenyl or naphthyl, and preferably it may be phenyl. 3

The cation M may be hydrogen, ammonium, or a metal. Typically M may be selected from the group consisting of hydrogen, ammonium, sodium, potassium, lithium, trivalent chromium, calcium, strontium, barium, magnesium, nickel, iron, and copper. Preferably, M may 35 be ammonium or an alkali metal e.g. sodium, potassium and lithium.

The group R may be a non-aromatic hydrocarbon containing at least 3 carbon atoms. Preferably, R may be selected from the group consisting of alkyl, cycloalkyl, alkenyl, and cycloalkenyl radicals. Preferably, R may contain at least 8, say 8-18 carbon atoms. Preferred R groups may include n-octyl, isooctyl, nonyl, decyl, undecyl, tridecyl, pentadecyl, heptadecyl octadecyl, 4-ethylcyclohexyl, octenyl, nonenyl, undecenyl, tridecenyl, pentadecenyl, heptadecenyl, 4-amylcyclohexenyl, etc.

The group R may be hydrogen, alkyl, aryl, aralkyl, omega-sulfonated alkyl, sulfonated aryl or sulfonated aralkyl. Preferably R may be omega-sulfonated alkyl, sulfonated aryl or sulfonated aralkyl and most preferably 5 R" may be selected from the group consisting of omegasulfonated lower alkyl (i.e. an alkyl containing less than about 6 carbon atoms), sulfonated phenyl and sulfonated benzyl. The sulfonated group contained in the R" group may typically be of the form MO S wherein M is as defined supra and preferably wherein M is alkali metal, e.g. sodium, potassium, ammonium or lithium.

The group R' may be hydrogen, alkyl or aralkyl. Preferably, R may be selected from the group consisting of hydrogen, lower alkyl (i.e. an alkyl containing less than about 6 carbon atoms) and benzyl. Most preferably, R' may be benzyl.

The group Y may be a solubilizing anion, typically a water-soluble anion. Preferably, Y may be selected from the group consisting of bromide, iodide, sulfate, acetate, methosulfate, ethosulfate, citrate, and perchlorate.

The sulfonated Z-alkylbenzimidazoles which may be present in the novel compositions of this invention may contain a quaternary nitrogen atom. Thus, a may be 1 and the compound may be a quaternized sulfonated Z-alkylbenzimidazole. When a is 0, the compound as added may contain no quaternized nitrogen atom. When the sulfonated 2-alkylbenzimidazole is added to the plating bath as an unquaternized compound, it may be converted in the acid bath to a quaternary compound. 7

3-omega-sulfo-n-propyl-benz- 3-sulfophenyl- It will be apparent to one skilled in the art that when R also contains a sulfonate group, this group may also be present in the ionized 0 5 form. The nitrogen atoms of the imidazole ring may also be present as ionized quaternary nitrogens in the highly acidic plating bath.

In practice of this invention one may use a mixture containing 5-95, preferably 30-90, say 66 parts by weight of the disulfonated alkyl diphenyl oxide and 5-95, preferably 10-70, say 33 parts by weight of the sulfonated benzimidazole. These materials may be readily mixed together in powdered form or in aqueous solution; and stored or used as such. The solutions may contain stabilizing amounts of a chromate or dichromate, of e.g., sodium or potassium to inhibit growth of fungi or mold.

The two components of the novel fume-suppressant composition may be preblended prior to their addition to the bath, or they may be added thereto individually. When added individually, they may be added as a solid or in separate aqueous solutions. Preferably, they may be preblended prior to the addition. Preblending may be accomplished by physically mixing the solid materials or by dissolving both of them in the same aqueous solution. This solution may typically contain about 120%, say 10%, by weight of the fume-suppressant composition. The dry materials may also be blended and compressed, i.e. pelletized, preferably together with a release agent, say sodium bicarbonate.

It has been discovered that when as little as 0.001 g./l. (grams per liter) of the novel anti-misting composition is added to a chromic acid bath in the chromium plating process, the amount of mist and spray is substantially reduced. Although these additives are stable in chromic acid baths, they do decompose to a slight extent and over a period of time are used up or depleted; drag out of solution further contributes to this depletion. The minimum initial amount added to the bath is to a large extent governed by the contemplated replenishment rate. It is also in part governed by cost considerations, by the amount of plating current used and by the actual construction of the plating tanks. Baths containing this additive develop a stable foam blanket on the surface. It is desirable that this blanket should be stable and of substantial, yet not too great, thickness, which could be dangerous because of the large amount of entrapped oxygen and hydrogen. For this reason the geometry of the plating system affects the desired concentration of additive as it will affect the thickness of the foam blanket for a given volume of bath. It is not contemplated that more than about 5 g./l. of the additive will be present in the bath at any one time. The bath may contain about 0.001 g./l. to 1.0 g./l. Larger amounts may be used but no apparent advantage may be realized thereby.

In typical embodiments of this invention, the novel fume-suppressant composition may be present in chromium plating baths in the amount of 0.001 to 1.0 g./l. of bath. Preferably, the composition may be present in the amount of 0.002 to 0.05, say 0.01 g./1. of bath.

It has been found that the anti-misting properties of the novel composition of this invention may endure over an extended period of time. This may be due in part to the unexpected synergistic action between the two components of the composition, thereby maintaining a substantially constant foam level for an indefinitely long period of time. It is a particular feature of this composition that presence of considerable excesses of this material (as by inadvertent overdosage) do not cause build up of any substantially excessive amount of foam.

Practice of the invention may be observed from the following examples wherein the parts are parts by weight unless otherwise noted. In this first series of three comparative examples, three anti-misting agents were prepared.

I. This agent was the Ultrav-on WC brand of the sodium salt of Z-n-heptadecyl, 3-sulfobenzyl benzimidazole sulfonate.

II. This agent was the Dowfax 2A1 brand of the mixture of disodium salts of monododecyl diphenyl oxide disulfonate and didodecyl diphenyl oxide disulfonate; and

III. This agent was a mixtureof 50%-50% of each of the agents of Examples I and II.

Each of these compositions was added in amount of l g./l. to one liter of a chromium plating solution having the following composition:

Component Concentration g./l.

Chromic acid 22S Sulfate 1 Silicofluoride 2 Ono foam 1very little foam 2-little foam 3-moderately little foam 4moderate foam 5-moderately high foam 6high foam 7-excessive foam 8very excessive foam FOAM RATING I II Houlrs at 45 C.:

A rating of 56 is preferred. A rating of 4 or below or 7 or above is undesirable. A rating below 3 or of 8 is unsatisfactory. From this table, it will be observed that the composition III of this invention permitted attainment of a desirable moderate foam blanket to about 75 hours while the composition II gave a satisfactory blanket for only 5 hours. The composition I gave undesirably high foam at the controlled concentrations of the test. It is particularly noteworthy that composition III gave a foam of substantially uniform thickness over a long period of time, while the foams produced by I and II varied widely or were excessive over the same period of time.

It is a further advantage of the novel compositions of this invention that they may produce less sulfate build-up in a commercial bath than fume-suppressants previously used. Sulfate ion is produced when the fume-suppressant breaks down in the plate bath. Since the compositions of this invention (e.g. composition III) may be effective for 68 times as long as previously used agents, they need not be added as frequently, and sulfate build-up may be thereby reduced.

It is a feature of this invention that use of the novel anti-misting agents of this invention is characterized by lower initial cost of production, production of more foam per unit weight of additive, longer foam life, lower concentration threshold of effectiveness, wider usable concentration range of operation, and their ability to produce durable foams of controlled and substantially constant thickness over extended periods of usage.

Although this invention has been illustrated by reference to certain specific embodiments, modifications thereof which are clearly within the scope of the invention will be apparent to those skilled in the art.

I claim:

1. A novel composition characterized by its ability to controllably develop and maintain over an extended period of time a fixed predetermined blanket of foam which consists essentially of a mixture of 5-95 parts by weight of a sulfonated 2-alkyl benzimidazole and 5-95 parts by weight of a disulfonated alkyl diphenyl oxide.

2. A novel composition characterized by its ability to controllably develop and maintain over an extended pe riod of time a fixed predetermined blanket of foam which consists essentially of (a) 5-95 parts of a disulfonated alkyl diphenyl oxide having the formula Q Q R. so x R a so tx wherein R is an alkyl group containing 6-18 carbon atoms; X is a cation selected from the group consisting of hydrogen, ammonium and metals; and n is 0l; and (b) 5-95 parts of a compound having the formula wherein Ar is selected from the group consisting of phenyl and naphthyl rings, said ring being incorporated into the imidazole structure through vicinal carbon atoms of said ring; M is a cation selected from the group consisting of hyrogen, ammonium and metals; R is a non-aromatic hydrocarbon containing 3-18 carbon atoms; R" is selected from the group consisting of omega-sulfonated lower alkyl, sulfonated phenyl and sulfonated benzyl; R' is selected from the group consisting of hydrogen, lower alkyl and benzyl; Y is a water-soluble anion; and a is 0-1.

3. A novel composition characterized by its ability to controllably develop and maintain over an extended period of time a fixed predetermined blanket of foam which consists essentially of (a) 30-90 parts of a disulfonated alkyl diphenyl oxide having the formula Q Rn SOQX R SOaX wherein Ar is selected from the group consisting of phenyl and naphthyl rings, said ring being incorporated into the imidazole structure through vicinal carbon atoms of said ring; M is a cation selected from the group consisting of hydrogen, ammonium and metals; R is a non-aromatic hydrocarbon containing 3-18 carbon atoms; R" is selected from the group consisting of omega-sulfonated lower alkyl, sulfonated phenyl and sulfonated benzyl; R'" is selected from the group consisting of hydrogen, lower alkyl and benzyl; Y is a water-soluble anion; and a is -1.

4. A novel composition as claimed in claim 3 wherein said compound is sodium 2-n-heptadecyl, 3-sulfophenyl benzimidazole sulfonate.

5. A novel composition as claimed in claim 3 wherein said compound is sodium Z-n-heptadecyl, 3-sulfobenzyl benzimidazole sulfonate.

6. A novel composition as claimed in claim 3 wherein said compound is sodium Z-n-heptadecyl, 3-omega-sulfon-butyl benzimidazole sulfonate.

7. A novel composition as claimed in claim 3 wherein the disulfonated alkyl diphenyl oxide is a mixture of disodium monododecyl diphenyl oxide disulfonate and disodium didodecyl diphenyl oxide disulfonate.

8. In the process for electrodepositing chromium from a chromium plating bath, the improvement which comprises maintaining in said bath a composition consisting essentially of 5-95 parts by weight of a sulfonated Z-alkyl benzimidazole and 5-95 parts by weight of a disulfonated alkyl diphenyl oxide, said composition being present in said bath in the amount of about 0.001-l.0 g./l.

9. In the process for electroplating chromium from a chromium plating bath, the improvement which comprises maintaining in said bath about 0.001-l.0 g./l. of a composition consisting essentially of (a) 5-95 parts of a disulfonated alkyl diphenyl oxide having the formula SOsX Rn R

RI! wherein Ar is selected from the group consisting of phenyl and naphthyl rings, said ring being incorporated into the imidazole structure through vicinal carbon atoms of said ring; M is a cation selected from the group consisting of hydrogen, ammonium and metals; R is a non-aromatic hydrocarbon containing 3-18 carbon atoms; R" is selected from the group consisting of omega-sulfonated lower alkyl, sulfonated phenyl and sulfonated benzyl; R' is selected from the group consisting of hydrogen, lower alkyl and benzyl; Y is a water-soluble anion; and a is 0-1.

10. In the process for electroplating chromium from a chromium plating bath, the improvement which comprises maintaining in said bath about 0.002-0.()5 g./l. of a composition consisting essentially of (a) 30-90 parts of a disulfonated alkyl diphenyl oxide having the formula @--4 at 803K wherein R is an alkyl group containing 6-18 carbon atoms; X is a cation selected from the group consisting of hydrogen, ammonium and metals; and n is 0-1; and (b) 10-70 parts of a compound having the formula Y t m wherein Ar is selected from the group consisting of phenyl and naphthyl rings, said ring being incorporated into the imidazole structure through vicinal carbon atoms of said ring; M is a cation selected from the group consisting of hydrogen, ammonium and metals; R is a non-aromatic hydrocarbon containing 3-18 carbon atoms; R" is selected from the group consisting of omega-sulfonated lower alkyl, sulfonated phenyl and sulfonated benzyl; R' is selected from the group consisting of hydrogen, lower alkyl and benzyl; Y is a water-soluble anion; and a is 0-1.

11. The process for electroplating chromium as claimed in claim 10 wherein said compound is sodium 2-n-heptadecyl, 3-sulfophenyl benzimidazole sulfonate.

12. The process for electroplating chromium as claimed in claim 10 wherein said compound is sodium Z-n-heptadecyl, 3-sulfobenzyl benzimidazole sulfonate.

13. The process for electroplating chromium as claimed in claim 10 wherein said compound is sodium Z-n-heptadecyl, 3-omega-sulfo-n-butyl benzimidazole sulfonate.

14. The process for electroplating chromium as claimed in claim 10 wherein the disulfonated alkyl diphenyl oxide is a mixture of disodium monodidodecyl diphenyl oxide disulfonate.

15. A novel bath for the electrodeposition of chromium comprising an aqueous acid chromium plating solution and, as an anti-misting agent, a composition consisting essentially of 5-95 parts by weight of a sulfonated Z-alkyl benzimidazole and 5-95 parts by weight of a disulfonated alkyl diphenyl oxide, said composition being present in said bath in the amount of about 0.0011.0 g./l.

16. A novel bath for the electrodeposition of chromium comprising an aqueous acid chromium plating solution and, as an anti-misting agent, 0.00l-1.0 g./l. of a composition consisting essentially of (a) 5-95 parts of a disulfonated alkyl diphenyl oxide having the formula Rn 803 R SOsX wherein R is an alkyl group containing 6-18 carbon atoms; X is a cation selected from the group consisting of hydrogen, ammonium and metals; and n is 0-1 and (b) 5-95 parts of a compound having the formula wherein Ar is selected from the group consisting of phenyl and naphthyl rings, said ring being incorporated into the imidazole structure through vicinal carbon atoms of said ring; M is a cation selected from the group consisting of hydrogen, ammonium and metals; R is a non-aromatic hydrocarbon containing 3-18 carbon atoms; R" is selected from the group consisting of omega-sulfonated lower alkyl, sulfonated phenyl and sulfonated benzyl; R is selected from the group consisting of hydrogen, lower alkyl and benzyl; Y is a water-soluble anion; and a is 0.1. 17. A novel bath for the electrodeposition of chromium comprising an aqueous acid chromium plating solution and, as an anti-misting agent, 0002-005 g./l. of a composition consisting essentially of (a) 30-90 parts of a disulfonated alkyl diphenyl oxide having the formula Rn SO3X R wherein R is an alkyl group containing 6-18 carbon atoms; X is a cation selected from the group consisting of hydrogen, ammonium and metals; and n is -1 and (b) 10-70 parts of a compound having the formula wherein Ar is selected from the group consisting of phenyl and naphthyl rings, said ring being incorporated into the imidazole structure through vicinal carbon atoms of said ring; M is a cation selected from the group consisting of hydrogen, ammonium and metals; R is a non-aromatic hydrocarbon containing 3-18 carbon atoms; R is selected from the group consisting of omega-sulfonated lower alkyl, sulfonated phenyl and sulfonated benzyl; R' is selected from the group consisting of hydrogen, lower alkyl and benzyl; Y is a water-soluble anion; and a is 0-1.

18. A novel bath as claimed in claim 17 wherein said compound is sodium Z-n-heptadecyl, 3-sulfophenyl benzimidazole sulfonate.

19. A novel bath as claimed in claim 17 wherein said compound is sodium 2-n-heptadecyl, 3-su1f0benzyl benzimidazole sulfonate.

20. A novel bath as claimed in claim 17 wherein said compound is sodium 2-n-heptadecyl, 3-omega-sulf0-nbutyl benzimidazole sulfonate.

21. A novel bath as claimed in claim 17 wherein the disulfonated alkyl diphenyl oxide is a mixture of disodium monododecyl diphenyl oxide disulfonate and disodium didodecyl diphenyl oxide disulfonate.

References Cited UNITED STATES PATENTS 2,036,525 4/1936 Granacher 2603()9.2 2,053,822 9/1936 Graenacher et al. 260309.2 2,854,477 9/1958 Steinhauer 260512 2,956,935 10/1960 Passal 260-51 JOHN H. MACK, Primary Examiner.

G. KAPLAN, Assistant Examiner. 

2. A NOVEL COMPOSITION CHARACTERIZED BY ITS ABILITY TO CONTROLLABLY DEVELOP AND MAINTAIN OVER AN EXTENDED PERIOD OF TIME A FIXED PREDETERMINED BLANKET OF FOAM WHICH CONSISTS ESSENTIALLY OF (A) 5-95 PARTS OF A DISULFONATED ALKYL DIPHENYL OXIDE HAVING THE FORMULA
 9. IN THE PROCESS FOR EELCTROPLATING CHROMIUM FROM A CHROMIUM PLATING BATH, THE IMPROVEMENT WHICH COMPRISES MAINTAINING IN SAID BATH ABOUT 0.001-1.0 G./1. OF A COMPOSITION CONSISTING ESSENTIALLY OF (A) 5-95 PARTS OF A DISULFONATED ALKYL DIPHENYL OXIDE HAVING THE FORMULA 